This project deals with the cytotoxic lymphocyte mediator, lymphotoxin, elaborated by stimulated lymphocyte which appears to be involved in cellular immune reactions such as tumor immunity. More specifically: 1) The investigation deals with the interaction of this mediator with the target cell plasma membrane. 2) The studies are concerned with previously demonstrated marked aberration in ribonucleic acid synthesis by lymphotoxin. This observation is now extended by examining the effect of a variety of inhibitors of RNA synthesis on lymphotoxin-treated cells. 3) The research will deal with the part played by lymphotoxin in tumor cell destruction by cellular immune reactions in the intact animal. Additional studies are underway to examine the role of lymphotoxin on lymphocyte-mediated cell destruction in tissue culture. 4) Work is in progress to determine cell type(s) elaborating lymphototoxins.